1. Field of the Invention
The present disclosure relates to the technical field of OLED manufacturing process, more specifically, to a method for improving the reflectivity of aluminum in OLED structure.
2. Description of the Related Art
In the technical field of OLED manufacturing process, the OLED is generally with the “sandwich” structure whose anode and cathode are respectively the ITO transparent electrode and the metal electrode. Driven by a certain voltage, electrons and holes are injected into the electron transport layer and the hole transport layer from the cathode and the anode respectively. Electrons and holes are transported to the light emitting layer through the electron transport layer and the hole transport layer respectively. Furthermore, the electrons and the holes meet with each other in the light emitting layer to form excitons. The excitons excite the light emitting molecules, thus the light emitting molecules emit the visible light after being radiated and relaxed. As shown in FIG. 1, generally, the “sandwich” structure of the anode of OLED is composed of a Top Layer 1, a Middle Layer 2 and a Bottom Layer 3. Top Layer 1 is covered by Top-ITO and acts as the anode of OLED. Middle Layer 2 adopts Ag as the reflective materials. Bottom Layer 3 is Bottom-ITO which acts as the contact material of the IC pad. The process machine is operated in the sputter coating mode.
In consideration of the oxidation characteristic of Ag material, it is necessary to divide Bottom-ITO and Ag/Top-ITO into two layers to define the pattern of the pixel area and the driver area individually. Besides, high reflectivity of Ag makes the processing of OLED color-adjustment be controllable. As shown in FIG. 2, as the oxidability of Ag is strong, the corrosivity is strong, it is easy to cause the concavities and hillocks, indicated as the white hollow triangles in the figure, on the surface of the metal layer, i.e., Middle Layer 2. The concavities and the hillocks will lead to a rough surface of the film and a poor quality of the film. However, the cost for using Ag as the target materials is 2 to 3 times higher than using Al, which increases the cost of manufacture. With respect to the metal Al, although the reflectivity of Al, lower or equal to 90%, is lower than Ag, the processing of Al is mature and it is already widely used in TFT-LTPS processing.
A related art has disclosed a top emission organic light emitting display with a reflective layer therein. The reflective layer, a first electrode, an organic layer and a transparent second electrode are subsequently formed on the substrate. When a bias voltage is applied to the first electrode and the transparent second electrode, the organic layer emits radiation. The reflective layer reflects radiation from the organic layer toward the transparent second electrode, and therefore the emission efficiency of the OLED increases.
Another related art has disclosed a self-illumination display, including a first substrate, a light-absorbing structure, a filter layer, a driving circuit unit and a self-illumination unit. The light-absorbing structure and the filter layer are disposed over the first substrate. The driving circuit unit is disposed over and shielded by the light-absorbing structure. The self-illumination unit is disposed over the filter layer, including a light-transmissible electrode, a light emitting layer and a black electrode. The self-illumination unit is disposed over the filter layer, including a light-transmissible electrode, a light emitting layer and a black electrode. The light-transmissible electrode is disposed over the filter layer while the light emitting layer and the black electrode are sequentially tiered on the light-transmissible electrode. The light-absorbing structure, the filter layer and the black electrode together reduce the reflection of the ambient light and enhance the image contrast. Consequently, it did not solve the problem that the concavities and hillocks will be formed on the surface of the metal aluminum film and reduce the reflectivity thereof